Polaris — The North Star — Is Breaking All the Astronomical Rules for Stars

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Further Study Into the Pulsing Behavior of The North Star, Polaris, Keeps Breaking Astronomical Models and Confounding Astronomers.

The common folk often confuse Polaris, aka The North Star, for the brightest star in the sky. Because for centuries humans looked for the North Star in the night sky as a means of navigation. If you found it, you knew you were headed North. That led to the idea that you just look for the brightest star. One has to wonder how many ill-informed wanderers looked up, found Sirus to be the brightest star, and followed it instead.

No. The ancients relied on Polaris because it appears almost directly above the North Pole. So, as the Earth turns, its position remains relatively constant. As such, Polaris looks nearly motionless, and always points a traveler north.

It also twinkles. Or rather, it pulses. 

Some such twinkling stars are called cepheids, and Polaris is the closest one to us. The reason Polaris pulses is that it makes up the bigger part of a binary star system. This means the North Star has a smaller sister star, Polaris B, that dances around her bigger sister in a dalliance we can spot from Earth.

Recently, however, scientists studying Polaris have discovered a major issue: Nobody can seem to agree on how big or how far away it is.

Calculating a Star

As with many areas in science, researchers use many methods for calculating a star’s mass, age, and distance. In the case of cepheids, the most common and heretofore accurate method is called the stellar evolution method. The stellar evolution method measures a star’s brightness, its spectrographic signature, and the rate at which it pulses. When the details are recorded, a few calculations later, scientists can come up with the precise age, distance, and mass of the cepheid. 

The reason many astronomers studying cepheids prefer the stellar evolution method is that the rate at which a cepheid pulses is directly related to its brightness. This makes calculating distance relatively easy and incredibly accurate. 

Unless you’re trying to measure the North Star.

The North Star is, Well, Different…

New research using a different calculation model shows some big discrepancies in what we thought we knew about Polaris. Because Polaris is so close—relatively speaking, of course—we can easily observe Polaris B’s orbit around the larger star. We know it takes about 26 Earth years to complete. And while we haven’t yet made a complete map of its orbit, we’ve observed enough to calculate its trajectory. Once they see the orbital pattern, scientists use Newton’s laws to determine the mass of each star.

By measuring Polaris’ mass that way, and combining those calculations with data from the Hubble Space Telescope’s parallax measurements, researchers estimate that Polaris is around 3.45 times more massive than our sun. This contradicts the predictions made by the stellar evolution model. In fact, stellar evolution predicts that Polaris should be around twice that big.

A Possible Solution?

Astronomers are baffled by the discrepancy in the calculations, but they admit that Polaris is incredibly difficult to study. For one thing, it’s position above the North Pole makes it difficult to observe clearly from many land-based telescopes. And the space telescopes are simply too sensitive to handle studying a star that close. It’s brightness nearly blinds the systems, which were meant to detect the dim light from objects halfway across the galaxy. 

So there aren’t many viable ideas on why these sets of data don’t match up. The one that seems to fit the models best seems to also be one of the more unlikely scenarios. You see, evidence points to the conclusion that Polaris B is an older star than it’s big sister. That’s not normally the case.

As such, some astronomers theorize that the Polaris we know and see today is actually two stars that fused together, which would essentially make a “new” looking star because of all of the excess energy and mass. Again, this scenario is unlikely, but not impossible. And until someone comes up with a better idea, it seems to be the most rational, if imperfect, explanation.

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Brandon Humphreys

Brandon Humphreys

I'm a wizard. I write stuff and it goes from my head into yours - Magic! Apart from that, I am the Senior Editor for Space Porn, a veteran, a rock guitarist, and a teacher.

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